11-20-2008 07:57 AM - edited 03-04-2019 12:26 AM
3825 running EBGP connects to WAN and IBGP to exchange with 3750.
3750 L3 switch has Four VLANs running iBGP
192.168.1.1 VLAN 1
192.168.2.1 VLAN 2
192.168.3.1 VLAN 3
192.168.4.1 VLAN 4
Should I have 4 sub interfaces on the router for the 4 VLANS on the switch?
Does anyone have a good example or reference?
The default gateways for the VLANs will reside on switch.
I can provide more info if needed
11-20-2008 08:15 AM
I prefer to connect L3 switches to routers using routed interfaces. The iBGP process can still use a loopback or physical interface of the L3 switch.
Hope that helps.
11-20-2008 08:26 AM
Thomas
I'm in total agreement with Collin on this. Pick and unused subnet for a P2P link between the 3750 and the 3825 eg. 192.168.5.0/30.
On the port connected to the 3825 router
int gi0/1
no switchport
ip address 192.168.5.1 255.255.255.252
and then config the 3825 interface
int gi0/1
ip address 192.168.5.2 255.255.255.252
This is so much simpler than creating vlan subinterfaces on your 3825 router.
Jon
11-20-2008 08:34 AM
All of your inter-vlan switching will happen on the L3 switch; all you need is a routed circuit between the router and L3 switch -- that is, on the 3750, you configure the uplink port as "no switchport", assign it an IP address in the same network as the IP on the Router's ethernet interface, and establish the routing protocol connection from that point.
I happen to be messing with BGP today, so I ask this based on my own "fun" in the lab -- why run BGP on the L3 switch? An IGP like OSPF or EIGRP would be just as simple and keep BGP at the edge of your network...
L3 Switch:
conf t
ip routing
! enables L3 switching
int f1/0/1
! uplink port
no switchport
ip address 10.0.0.2 255.255.255.0
no shut
! turns off the 'switching' function of the port and enables ip routing on it, asssigns an ip address, etc
router bgp 65000
neighbor 10.0.0.1 remote-as 65000
network 192.168.1.0 mask 255.255.255.0
! repeat for the rest of the networks -- or I *think* "REDISTRIBUTE CONNECTED" will work too
no auto-summary
interface VLAN 1
ip add 192.168.1.1 255.255.255.0
interface VLAN 2
ip add 192.168.2.1 255.255.255.0
! and so on... hosts connecting to ports on the switch are set to access whatever VLAN and their default gateway should be configured as the interface VLAN supporting the VLAN they are assigned to
On the router-
conf t
int f0/0
! port to 3750
ip address 10.0.0.1 255.255.255.0
no shut
router bgp 65000
! in addition to WAN-pointing BGP statements
neighbor 10.0.0.2 remote-as 65000
network 10.0.0.0 mask 255.255.255.0
I haven't tried this specific config in a lab, but it should be close...
11-20-2008 09:33 AM
You have a good point. I am thinking it was never brought up in discussion is the reason that we are using BGP instead of EIGRP or OSPF for the IGP. I will run it by management. Thanks all for your replies. They definitely helped in making a decision.
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